Method for forming a carbide layer of a IV-b group element of the periodic table on the surface of a cemented carbide article

ABSTRACT

A method for forming a carbide layer of a IV-b group element of the periodic table on the surface of a cemented carbide article in a treating molten bath, comprising preparing a treating molten bath composed of molten boric acid or borate and a IV-b group element dissolved therein and immersing the article in the treating molten bath to deposit the IV-b group element on the surface of the article and to form a carbide layer of the IV-b group element on the surface of the article with the carbon contained in the article. The method of this invention can form easily a smooth and hard carbide layer on the surface of the article. And the formed layer improves greatly the hardness and wear resistance of the cemented carbide article.

United States Patent Komatsu et al.

METHOD FOR FORMING A CARBIDE LAYER OF A IV-B GROUP ELEMENT OF THEPERIODIC TABLE ON THE SURFACE OF A CEMENTED CARBIDE ARTICLE Inventors:Noboru Komatsu, Toyoakeshi;

Tohru Arai, Nagoyashi; Yoshihiko Sugimoto, Nagoyashi; MasayoshiMizutani, Nagoyashi, all of Japan Kabushiki Kaisha Toyota ChuoKenkyusho, Nagoyashi, Japan Filed: Apr. 11, 1974 Appl. No.: 460,148

Assignee:

Foreign Application Priority Data Apr. 12, 1973 Japan 48-40821References Cited UNITED STATES PATENTS 8/1959 Goetzel et al 117/1183,744,979 7/1973 Kalish 117/127 Primary ExaminerMayer WeinblattAssistant ExaminerEdith L. Rollins Attorney, Agent, or Firm-Wenderoth,Lind & Ponack [5 7] ABSTRACT A method for forming a carbide layer of alV-b group element of the periodic table on the surface of a cementedcarbide article in a treating molten bath, comprising preparing atreating molten bath composed of molten boric acid or borate and a IV-bgroup element dissolved therein and immersing the article in thetreating molten bath to deposit the IV-b group element on the surface ofthe article and to form a carbide layer of the IV-b group element on thesurface of the article with the carbon contained in the article. Themethod of this invention can form easily a smooth and hard carbide layeron the surface of the article. And the formed'layer improves greatly thehardness and wear resistance of the cemented carbide article.

7 Claims, 2 Drawing Figures PATENTED 3,885,059

SHEET 10F 2 FIG.1

METHOD FOR FORMING A CARBIDE LAYER OF A IV-B GROUP ELEMENT OF THEPERIODIC TABLE ON THE SURFACE OF A CEMENTED CARBIDE ARTICLE Thisinvention relates to a method for forming a carbide layer ofa lV-b groupelement of the periodic table on the surface of a cemented carbidearticle, and more particularly it relates to the formation of thecarbide layer on the surface of the article immersed in a treatingmolten bath. The cemented carbide with the carbide layer formed thereonhas a greatly improved hardness, wear resistance and machinability.

Cemented carbide tools having a carbide layer such as titanium carbide(TiC) and zirconium carbide (ZrC) have been reported to have aremarkably improved cutting ability and have come to be used practicallyin these years.

As a practical method for forming a titanium carbide on the surface of acemented carbide article, a chemical vapor deposition method has beenemployed. Said coating is to heat an article to be treated in a hydrogenatmosphere containing the vapor of titanium chloride (TiCl andhydrocarbon such as propane, benzene and butane. In this coating, sincetitanium and titanium chloride are easily oxidized in an atmospherecontaining oxygen or water, the atmosphere must be carefully prepared toexclude oxygen and water from the atmosphere. Also since said atmospherecontains a corrosive titanium chloride and dangerous hydrogen gas, theconstruction of a treating furnace becomes to be complicated. Therefore,the operability of the method is not good and the treating cost isrelatively high. The conventional method for forming a zirconium carbidelayer has the same drawbacks as those of the above mentioned method forforming a titanium carbide.

Therefore, it is the principal object of this invention to provide animproved method for forming a carbide layer of a lV-b group element onthe surface of a cemented carbide article in a treating molten bath.

It is another object of this invention to provide a method for forming acarbide layer, which is safe and simple in practice and less expensive.

Other objects of this invention will appear hereinafter.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The invention,itself, as to its method of operation, together with additional objectsand advantages therefore, will best be understood from the followingdescription of specific embodiments when read in connection with theaccompanying drawings, in which:

HO. 1 is a photomicrograph showing a titanium carbide layer formed on acemented carbide according to Example 4;

FIG. 2 is an X-ray diffraction chart of the layer formed on the surfaceof a cemented carbide according to Example 4.

Broadly, the present invention is directed to an improvement of themethod for forming a carbide layer of a lV-b group element of theperiodic table on the surface of a cemented carbide article in atreating mol ten bath composed of molten boric acid or borate and a lV-bgroup element dissolved therein. Namely, the method of the presentinvention comprises preparing a treating molten bath composed of boricacid or borate and a lV-b group element dissolved therein and immersinga cemented carbide article in the treating molten bath for forming avery hard carbide layer of said lV-b group element on the surface ofsaid article. During the treatment, it is believed that the dissolvedlV-b group element in the treating molten bath reaches to the surface ofthe article and deposit on the article for forming the carbide layerwith the carbon contained within the article.

As the bath material, a mixture of boric acid (B 0 and/or borate such aspotassium borate borax (K 8 0 and sodium borate (Na B O with a lV-bgroup element is used. The boric acid and borate can melt at arelatively low temperature and dissolve easily a lV-b group element inthe molten boric acid or borate. Moreover they act as a kind of fluxcapable of keeping the surface of an article to be treated in its cleanand fresh state and suppressing the formation of oxide thereon.Therefore, the treating molten bath containing boric oxide or borategives a smooth and uniform carbide layer on the surface of the article.

As the lV-b group elements, one or more elements of titanium, zirconiumand hafnium can be dissolved in the molten boric acid or borate.

In order to prepare the treating molten bath, any of the following meanscan be preferably employed.

1. It is to introduce a metallic powder or thin plate of a lV-b groupelement or of an alloy containing a lV-bgroup element into a moltenboric acid or borate bath. 2. It is to introduce a powder or thin plateof the halide ofa lV-b group element into a molten boric acid or boratebath.

3. It is to dissolve anodically a plate or a block of a IV-b groupelement or of an alloy containing a lV-b group element in a molten boricacid or borate bath by applying an electric current to the bath with useof the plate as an anode.

The f rst means utilizes the property of the molten boric acid andborate to dissolve a lV-b group element. This means is easy inoperation. However, the velocity of the dissolution of the element intothe bath is relatively slow. To accerelate the dissolution, the elementshould be in a shape having a large contact area. From this point ofview, a fine powder (of under 20 mesh) is much preferable than a thinplate. With use of a fine powder, a part of undissolved powder will befloat in the treating molten bath and worsen the smoothness of thesurface of an article to be treated by sticking to said surface. Theother part of undissolved powder will be piled up on the bottom of thevessel holding the treating molten bath and reduce the effective spaceof the treating molten bath. As a source of a lV-b group element, a puremetal of the element is much preferable than an alloy of the element.Another metallic element contained the metal or alloy of a lV-b groupelement will react with cemented carbide forming an article to betreated and suppress the formation of a good carbide layer of the IV-bgroup element on the surface of the article. 5 percent by weight(hereinafter percent means percent by weight) of a IV-b group element inthe treating molten bath is sufficient. In practice, however, the lV-bgroup element may be contained in the treating molten bath in a quantitybetween about 1 50 percent (the quantity of boric acid or borate beingwithin a range from 50 to 99 percent). With use of less quantity of aIV-b group element than 1 percent, the speed of formation of the carbidelayer would be too slow to be accepted for the practical purpose. Toomuch addition of a lV-b group element than 50 percent will increase theviscosity of the treating molten bath and brings the drawbacks mentionedabove due to the increase of undissolved powder of the element.

The second means is to use a halide of a lV-b group element such as TiClTiF,;, Til Na TiF,,-, Na- ZrF HfF HfCl The halides can be dissolvedeasily and completely without leaving undissolved particles in themolten boric acid or borate so that the operability of the treatmentincreases and the sticking of undissolved particle to the surface of thearticle is avoided. As the shape of the halide, the shape of powder orthis plate is preferable as same as the shape of the metal of lV-b groupelement mentioned in the first means. Since the halide is dissolvedquickly, the size of the powder is not necessary to be as fine as themetallic powder in the first means.

The halide may be contained in the treating molten bath in a quantitybetween about 1 and 50 percent.

The third means is to dissolve anodically a plate or block of a IV-bgroup element or of an alloy of the element in the molten bath by use ofthe plate or block as an anode and use of the vessel holding the bath oran electric conductive material dipped in the bath as a cathode. In thiscase, the speed of the dissolution of the element is very fast comparedwith that of the powder of the element, and the drawbacks caused fromundissolved powder in the first means are avoided completely. The speedof'dissolution of the element is increased according to the increase ofthe current density applied to the anode. However the element isdissolved without applying a current to the anode. Therefore, thecurrent density is not necessary to be large. The practical anodiccurrent density is within from 0.1 to A/cm The treatment of theinvention is accomplished by dipping and keeping a cemented carbidearticle to be treated in the treating molten bath prepared by any of themeans mentioned above.

In the third means, preparing the treating bath, by the anodicdissolution of a IV-b group element and the treating of the article canbe carried out at the same time. In this case, the article to be treatedmust be immersed in the bath without being contacted with both of theanode and cathode.

Also the treating molten bath prepared by the third means can besolidified by cooling and kept without worsening the quality of thetreating material. When the treatment is necessary, the treatingmaterial can be heated up to the treating temperature to prepare thetreating molten bath and the treatment can be carried out with use ofthe treating molten bath.

The IV-b group element dissolved in the treating molten bath reacts withthe carbon contained in the cemented carbide forming the article to betreated and forms a carbide layer on the surface of the article.

As the vessel holding the treating molten bath, a vessel made of thematerial which does not react with the treating molten bath and has ahigh melting point, such as graphite, heat resistant steel and nitridecan be used. From the practical point, the vessel made of graphite orheat resistant steel is preferable.

Here, cemented carbide forming an article to be treated means a sinteredtungsten carbide containing cobalt. Said cemented carbide may include asmall amount of titanium carbide, niobium carbide. tantalum carbide andthe like.

The treating temperature may be selected within the range from theliquidified point of the treating molten bath to the melting point ofthe article to be treated. From the view of practical forming speed ofthe layer, the treating temperature is preferably 900C or higher than900C. From the point of deterioration of the quality of the materialforming the article during the treatment, the treating temperature ispreferably 1200C or lower than l2()OC.

A small amount of halide such as NaCl, KC] and NaF. oxide such as P 0hydroxide such as NaOH and KOH, sulfate, carbonate or nitrate can beadded into the treating molten bath to lower the viscosity of the bath.

The treating time depends upon the thickness of the carbide layer to beformed, Heating shorter than 1 hour, however, provide no practicallyaccepted formation of said layer. With the increase of the treatingtime, the thickness of the carbide layer will be increasedcorrespondingly. In practise, an acceptable thickness of the layer canbe realized within 30 hours or shorter time.

It is not necessary to carry out the method of the present invention inthe atmosphere of non-oxidation gas, but the method can be carried outinto effect either under the air atmosphere or the inert gas atmosphere.

EXAMPLE I 500 grams of borax powder was introduced into a graphitecrucible and heated up to lOOOC for melting the borax in an electricfurnace, and then about 110 grams of metallic titanium flakes of 0.5mmthick was added into the molten borax. Thus a treating molten bath wasprepared.

Next, a specimen, 1.0 X 5.5 X 30mm, made of cemented carbide composed of91 percent of tungsten carbide and 9 percent of cobalt was dipped intothe treating molten bath kept therein for 15 hours, taken out therefromand air cooled. The treating material adhered to the surface of thespecimen was removed by washing with hot water and then the specimentreated was investigated. After cutting and polishing the specimen, thespecimen was micrographically observed, and a layer of about 10 micronsthick was found on the surface of the specimen. By X-ray diffractionmethod, strong diffraction lines'of titanium carbide (TiC) were foundfrom the formed layer and the layer was identitied to be titaniumcarbide. By a micro vickers hardness tester, the formed layer wasmeasured to be about Hv 3l80. Compared with this the specimen before thetreatment was measured to be about H'v I525.

EXAMPLE 2 In the same manner as described in Example 1, a treatingmolten bath was prepared by introducing 10 percent of metallic zirconiumpowder of under' ZO mesh into percent of molten borax. Next a specimenhaving the same shape and made of the same material as those of thespecimen treated in Example I was dipped in the treating molten bath,kept therein for 16 hours at l000C, taken out therefrom and air cooled.By the treatment, the specimen was formed with a layer of about 10microns. The layer was tested'by X-ray diffraction method anddiffraction lines corresponding to zirconium carbide (ZrC) were clearlydetected. The

hardness of the treated specimen was measured to be about Hv 2750.

EXAMPLE 3 ln the same manner as described in Example 1, 500 grams ofmolten borax was prepared in a graphite crucible and then a rod havingmm diameter and made of titanium was dipped in the molten borax andanodically dissolved into the molten borax by applying an electriccurrent to the molten borax through the rod used as an anode and thecrucible used as a cathode for 2 hours with an anodic current density of3 A/em By the anodic dissolution, a treating molten bath was prepared.The content of titanium dissolved in the treating molten bath wascalculated to be about 8.3 percent.

Next, a specimen having the same shape and made of the same material asthose of the specimen used in Example l was dipped in the treatingmolten bath, kept therein for l6 hours at lO0OC, taken out therefrom andair cooled. By this treatment, the specimen was formed with a titaniumcarbide (TiC) layer of about 12 microns on the surface thereof.

EXAMPLE 4 100 grams of borax powder was introduced into a graphitecrucible and heated up to lO0OC for melting the borax in an electricfurnace, and then about 76 grams of Na TiF powder of under 100 mesh wasintroduced into the molten borax, thus a treating molten bath containingabout 10 percent of titanium was prepared. Next a specimen having thesame shape and made of the same cemented carbide as those of thespecimen used in Example 1 was clipped in the treating molten bath, kepttherein for hours at lO0OC, taken out therefrom and air cooled. By thetreatment, a layer having an about 10 microns thick and shown in thephotomierograph of FIG. 1 was formed on the surface of the article. ByX-ray diffraction method, a diffraction chart shown in FIG. 2 was givenfrom the formed layer. The chart shows strong diffraction lines oftitanium carbide. Also the layer was identified to contain a largequantity of titanium by X-ray micro analyzer.

The hardness of the treated specimen was measured to be about Hv 3070.

EXAMPLE 5 In the same manner as described in Example 4, a treatingmolten bath containing 10 percent of zirconium by introducing about 39grams of ZrCL, powder of under mesh into lOO grams of molten borax.Then, a specimen having the same shape and made of the same cementedcarbide as those of the specimen used in Example 1 was dipped in thetreating molten bath, kept therein for 15 hours at lO0OC, taken outtherefrom and air cooled. By the treatment, a layer of about 5 micronswas formed on the surface of the article. From the formed layer,diffraction lines corresponding to the lines of zirconium carbide (ZrC)were detected. The hardness of the treated specimen was measured to beabout Hv 2750.

What is claimed is:

l. A method for the surface treatment of a cemented carbide article,comprising the steps of preparing a treating molten bath consistingessentially of boric acid or borate and a substance containing at leastone element of the group consisting of titanium, zirconium and hafniumand immersing the article in the treating molten bath, thereby forming acarbide layer of said element on the surface of the article thustreated.

2. A method according to claim 1, wherein said borate is selected fromthe group consisting of sodium borate and potassium borate.

3. A method according to claim 1, wherein said substance is a metallicpowder or a thin plate containing said element and said treating moltenbath is composed of l to 50 percent by weight of said metallic powder orthin plate and the rest of boric acid or borate.

4. A method according to claim 1, wherein said substance is a halide ofsaid element and the treating molten bath is composed of l to 50 percentby weight of said halide and the rest of boric acid or borate.

5. A method according to claim 4, wherein said halide is selected fromthe group consisting of TiCl TiF Til Na- TiF N21 ZrF HfF and HfCl 6. Amethod according to claim 1, wherein said treat ing molten bath isprepared by the steps of melting boric acid or borate in a vessel,dipping a metallic plate containing said element and dissolvinganodically said metallic plate or block into the molten boric acid orborate with an anodic current density within a range from 0.1 to 10 A/cm7. A method according to claim 1, wherein said cemented carbide articleis made of tungsten carbide and

1. A METHOD FOR THE SURFACE TREATMENT OF A CEMENTED CARBIDE ARTICLE,COMPRISING THE STEPS OF PREPARING A TREATING MOLTEN BATH CONSISTINGESSENTIALLY OF BORIC ACID OR BORATE AND A SUBSTANCE CONTAINING AT LEASTONE ELEMENT OF THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM AND HAFNIUMAND IMMERSING THE ARTICLE IN THE TREATING MOLTEN BATH, THEREBY FORMING ACARBIDE LAYER OF SAID ELEMENT ON THE SURFACE OF THE ARTICLE THUSTREATED.
 2. A method according to claim 1, wherein said borate isselected from the group consisting of sodium borate and potassiumborate.
 3. A method according to claim 1, wherein said substance is ametallic powder or a thin plate containing said element and saidtreating molten bath is composed of 1 to 50 percent by weight of saidmetallic powder or thin plate and the rest of boric acid or borate.
 4. Amethod according to claim 1, wherein said substance is a halide of saidelement and the treating molten bath is composed of 1 to 50 percent byweight of said halide and the rest of boric acid or borate.
 5. A methodaccording to claim 4, wherein said halide is selected from the groupconsisting of TiCl3, TiF6, TiI4, Na2TiF6, Na2ZrF6, HfF4 and HfCl4.
 6. Amethod according to claim 1, wherein said treating molten bath isprepared by the steps of melting boric acid or borate in a vessel,dipping a metallic plate containing said element and dissolvinganodically said metallic plate or block into the molten boric acid orborate with an anodic current density within a range from 0.1 to 10A/cm2.
 7. A method according to claiM 1, wherein said cemented carbidearticle is made of tungsten carbide and cobalt.